(1) Field of the Invention
The present invention relates to a phase-change information recording medium and an optical recording method which records information to the phase-change information recording medium.
(2) Description of the Related Art
A phase-change information recording medium which utilizes a phase change of a recording layer made of a phase-change alloy, between the crystalline phase and the amorphous phase is known as one of optical information recording media that are capable of reading, writing and erasing of information by the application of light, such as a laser beam, to the recording layer. In the phase-change information recording medium, the entire recording layer is initially set in the crystalline phase. The laser beam is locally emitted to a portion of the recording layer in the recording medium, and the recording layer portion is heated above the melting point of the recording layer by the light energy, and rapidly cooled so that the recording layer portion is set in the amorphous phase.
In a conventional recoding method for the information recording media of the above type, a data signal is supplied to a semiconductor laser of an optical pickup through pulsewidth modulation (PWM), so that the laser is operated in accordance with a controlled power supplied to the laser so as to emit a laser beam to the recording layer of the recording medium. In this manner, a sequence of amorphous/crystalline phases is created along the track of the recording medium so that the data signal is encoded in the recording medium.
The standard requirements for rewritable compact disk have been provided by the so-called orange book, part III. The rewritable compact disk is a type of the above-mentioned information recording media. According to the standard requirements, the linear rotation rate of the rewritable compact disk is to be in a range from 2.4 m/s to 2.8 m/s. This linear rotation rate is only twice as large as the basic linear rotation rate which is in a range from 1.2 m/s to 1.4 m/s.
However, with recent development of personal computers with high-speed data processing performance, there is an increasing demand for an improved phase-change information recording medium for use in the recent personal computers which can achieve the reading, writing and overwriting of information at higher rotation rates than those achieved by a conventional phase-change information recording medium. In addition, it is desirable to establish an optical recording method which can achieve the reading, writing and overwriting of information for the improved phase-change information recording medium at the higher rotation rates without significant degradation.